Up to now, the dyeing of cellulose fiber was carried out with a reactive dye at pH 10 and over in the presence of an acid capturing agent such as sodium carbonate, potassium carbonate, sodium hydroxide and the like and an electrolyte such as sodium chloride, sodium sulfate and the like at a temperature of about 100.degree. C. and below.
However, since in recent years the demand for the mixed spinning of cellulose with other fibers, especially polyester fiber, is increasing, it is necessary to employ dyes and dyeing conditions suitable for cellulose and polyester fibers respectively, for dyeing of such cellulose/polyester mixed fiber (hereinafter merely referred to as c/p fiber). This is because the dye and dyeing conditions for polyester fiber are considerably different from those for cellulose fiber. That is, it is necessary to use a disperse dye for the dyeing of polyester fiber at a temperature of about 130.degree. C.
If the c/p fiber above is dyed in the same process at once, for example, the dyeing has to be carried out by using two different dyes and by means of a combination of a reactive dye and a disperse dye, but it has some problems. For example, in order to exhaust the cellulose fiber part fully with a reactive dye, the pH value has to be kept at 10 and over by the addition of an acid capturing agent. However, the presence of the acid capturing agent accelerates the decomposition of the disperse dye to give poor exhaustion of the polyester fiber part. On the other hand, a high temperature condition is required in order that the polyester fiber part is exhausted by a disperse dye. However, the hydrolysis of the disperse dye is accelerated under the high pH value stated above and the high temperature, and thus, exhaustion of the cellulose fiber becomes extremely inferior. Accordingly, the two-bath method, that is, one of cellulose or polyester fiber is dyed first and then the other is dyed by another bath, has been generally employed for dyeing of c/p fiber.